Electrostatographic developing apparatus



L. F. W. LAWES ETAL ELECTROSTATOGRAPHIC DEVELOPING APPARATUS Feb. 6, 1 968 2 Sheets-Sheet 1 Filed June 1, 1966 Feb. 6, 1968 1.. F. w. LAWES ETAL 3,357,307

ELECTROSTATOGRAPHIC DEVELOPING APPARATUS 2 Sheets-Sheet 2 Filed June 1; 1966 United States Patent 3,367,307 ELECTRGSTATOGRAPHIQ DEVELOPFNG APPARATUS Louis Frederick Wiliiam Lawes, Walton-on-Thames, Surrey, and Nicholas Gilbert Shreeve and Naudor Mihalik, Weybridge, Surrey, England, assignors to Arlsitle Limited, Maidenhead, England, a British company Filed June 1, 1966, Ser. No. 554,591 Claims priority, application Great Britain, dune 2, 1965, 23,539/65 8 Claims. ((3. 1l8637) ABSTRACT 0F THE DISCLOSURE In electrostatographic copying apparatus, developer apparatus for cascading developer material over a surface to develop a latent image thereon, and for recirculating said developer material for subsequent re-use, comprises a continuously operative conveyor which returns cascaded material to a hopper; the hopper has a shutter which is opened only intermittently, to allow developer material to cascade therefrom over said surface when there is an image thereon which is to be developed.

This invention relates to an apparatus for applying developer to an electrostatographic surface so that an electrostatographic latent image thereon may be developed.

In an electrostatographic process, a latent image formed on an electrostatographic surface is developed by the application of a suitable developer so that the latent image is rendered effective and usually, but not necessarily, visible. Among methods by which this may be done is that generally known as cascade development. In cascade development, a developer comprising carrier particles and developer powder carried thereby is flowed over the latent image bearing surface in such manner that the powder is removed from the carrier particles by the latent image, but not by the background area of the surface nor by any small residual forces remaining on said surface, resulting in a print of good clarity and line. It has previously been proposed to effect cascade development by tipping developer from drawers or traps or by lifting the developer by buckets or similar means from a reservoir and allowing it to cascade down the electrostatographic surface back to the reservoir. It has also been proposed to throw the developer by fan blades on to the latent image bearing surface.

According to the present invention there is provided apparatus for supplying developer material to an electrostatographic surface to cascade thereover and develop a latent image carried thereon, and for recirculating the developer material for subsequent reuse, comprising deflector means arranged to guide to a lower region developer material falling from the said surface after cascading thereover, conveyor means arranged to raise such developer material from said lower region and to discharge it at an upper region, a hopper comprising an inclined base having a rear end disposed below the said upper region to collect the developer material discharged there and a front end disposed obliquely below said rear end whereby developer material collected on the rear end moves by gravity towards the front end to be discharged therefrom to the said surface, a shutter arranged to cooperate with the hopper base near the front end thereof to prevent discharge of developing material therefrom, and means controlled separately from and independently of operation of said conveyor means for opening the shutter to allow such discharge from said hopper when required.

The elevator means may comprise a rotatable circular member with a hub member rotatably mounted with its axis perpendicular to that of a drum on which the electrostatographic member is provided, the elevator being provided at its periphery with circumferentially spaced scoops adapted to collect developer from the receiving chamher at the bottom of its travel and to rotationally lift and deliver by gravity fall into the storage hopper at the top of its travel.

The elevator means may either be located within a separate container comprised by the developing apparatus, or it may of itself constitute a rotating wall of such a container.

The means for regulating the rate of discharge of developer from the hopper may comprise a shutter adjustable to control an aperture at the base of the storage hopper through which aperture developer is discharged on to the electrostatographic surface.

The developer may comprise simply conventional developer powder or it may comprise developer powder mixed with a carrier mixture such as glass beads and in correct tribo-electrical relationship therewith. The precise nature of the developer is immaterial to the present invention, provided that it is in fine flowing form.

In order that the invention may be more fully understood, embodiments are now described with reference to the accompanying drawings, in which:

FIGURE 1 shows diagrammatically a first embodiment of developer apparatus according to the invention, in association with a drum of which the surface is adapted to hear an electrostatographic image to be developed;

FIGURE 2 shows diagrammatically a second embodiment of developer apparatus according to the invention, in association with another similar drum;

FIGURE 3 shows diagrammatically a powder replenisher device which may be comprised by the developer apparatus shown in FIGURE 1 or FIGURE 2;

FIGURE 4 is a vertical sectional view, on a larger scale, of a practical embodiment of a developer apparatus according to the invention and substantially in accordance with FIGURE 1; and

FIGURE 5 shows, diagrammaticaly and on a reduced scale, a front view of the relationship to one another of parts of the developer apparatus shown in FIGURE 4.

Referring now to FIGURE 1, a drum 1, of which the surface may have produced on it an electrostatographic image by means not shown, is rotatable in the direction indicated by an arrow 2, by a main drive means (not shown) of electrostatographic apparatus in which the drum is incorporated. At its ends, the drum 1 is formed with annular grooves or recesses 3 into which project the forward edges 4 of side plates 5 of developing apparatus according to the invention. The edges 4 are preferably provided with sealing strips of felt or the like to prevent any cascading developer from escaping in a lateral direction. The side walls 5 are parts of a container which also has a back wall 6 and within which is mounted a rotary elevator 7 on a shaft 8 through which it is driven by the said main drive means, the axis of rotation of the elevator being at right angles to that of the drum 1. The elevator 7 is circular in shape, and is provided round its periphery with spaced scoops 9. The developing apparatus comprises a storage hopper 10 in which developer, preferably a mixture of carrier particles and developer powder carried thereby, is stored. As a latent image formed on the electrostatographic drum 1 approaches the developing station, an electrical impulse is caused, as further described below, to operate a solenoid 11 of the developer apparatus thereby to open a shutter 12 thereof. Developer from the hopper 10 then cascades down the electrostatographic surface as it rotates, causing the latent image thereon to be developed. The rate of flow of the developer can be controlled by governing the opening of the shutter 12, to allow a smaller or larger opening. After the developer has cascaded down the image bearing surface, it is directed by deflector plates 13 and 14 into the lower part of the elevator 7 whence it is scooped up by the scoops 9. It will be readily appreciated that the greater part of the developer will be directed by the deflector plate 13, the plate 14 serving to catch the remainder. Of course, any number of deflector plates may be fitted as may be necessary. As the elevator rotates, the scoops lift up the developer which is lodged in them until it eventually falls by gravity on to a collecting plate 15 which returns it to the hopper 10. It will be appreciated that at this point the width of the collecting plate 15 is narrower than the width of the drum 1, and thus of the storage hopper at the aperture provided by raising the shutter 12. Although the natural forces acting on the developer cause it to spread more or less evenly across the collecting plate 15, it is preferable to employ a spreader 16, which not only serves to actively promote even distribution, and to prevent excessive pileup of developer composition on the collector plate 15, but also, as will subsequently appear, to assist in developer powder replenishment. The spreader, which is driven at suitable speed by the main drive means which also, as already described, rotates the drum 1 and the elevator 7, can be of any convenient design, such as a polygonal or fan shaped rod; but preferably the spreader consists of a two-way screw, so that the developer composition is constantly being spread outwards from the centre toward the edges of the plate 15. The powder is replenished by a device 17, which dispenses measured quantities of fresh powder in cloud form on to the developer returned to the plate 15, so that the spreader serves to effectively mix the replenishment powder into the developer. This replenishment is only operative for a limited time for each occasion on which the storage hopper shutter is opened, so that only sufficient replenishment powder is added to compensate for the powder removed during the development of the image; additional means may if desired be provided to control the quantity of powder added during a given replenishment operation, so that more powder may be added when large areas have to be developed. As soon as the image area has passed out of the development station, the shutter 12 is closed by terminating the electrical impulse which held the solenoid 11 energized. The speed of the elevator 7 is adjusted to ensure even distribution, and the balance of speed and quantity of developer is such that the storage hopper 10 is never empty either during or after development of an image on the drum. The tumbling action of the developer during the whole process, especially in the elevator, ensures that a completely even balance is achieved between powder and carrier particles, and that the correct triboelectrical properties are imparted.

In the embodiment shown in FIGURE 2, the operation is identical with that previously described for FIG- URE 1, and the same reference numbers are used for corresponding parts in FIGURES 1 and 2, except that there is no backplate to the container 5, the rear wall of the elevator 7 itself constituting the back of the developer apparatus. A suitable seal 18, of felt for example, is provided between the elevator and the stationary parts of the apparatus to prevent any possible escape of developer.

The powder replenishing device 17 of FIGURES 1 and 2 may be as illustrated in FIGURE 3 and thus substantially similar to the developer disclosed in our copending United States patent application Ser. No. 474,743 filed July 26, 1965. As shown in FIGURE 3, fresh developer powder is stored in a hopper 18, which can be refilled through an aperture, in the top, which is normally closed by a lid. Inside the hopper, at its lower end, is a roller 19 which rotates in the direction indicated by an arrow. The roller 19 has a smooth surface in which are formed spaced dimples of selected size so that as the roller rotates uniform calculated quantities of powder are picked up in each dimple. An agitator 20 ensures that there is no tunneling in the powder and that it fills the dimples regularly and evenly; it also serves to break up any conglomerations of powder which may tend to be formed due to the weight of the powder pressing down. The dimpled roller rotates past a knife edge 21, which removes any excess powder, into a cloud chamber wherein is located a brush 22. The brush, which is selected of material to give the correct tribo-electric relationship with the powder, rotates at a controlled speed in the direction shown by an arrow, presses into the dimpled roller and picks up all the powder from the dimples. The brush then rotates past a flick rod 23 which causes it to discharge a cloud of powder 24 at the powder-depleted developer discharged by the elevator 7 on to the collecting plate 15 and there being spread by the spreader 16. The quality of the cloud discharged is governed by the number, size and shape of the dimples, and the speeds of the dimpled roller and brush. With a given replenisher, the rate at which powder is dispensed by the replenisher may be simply controlled by a variable speed device governing the speed of the rotation of the dimpled roller and brush. It will be appreciated that although it is preferred to use a replenisher as shown in FIGURE 3, with its advantages of ensuring that the powder is replenished in its finest form, without any lumps or conglomerated particles which reduce the efficiency of the cascade system, it is nevertheless within the scope of the present invention to provide a developing system in accordance with FIGURE 1 or FIGURE 2 but having associated with it a replenisher of some other kind.

FIGURES 4 and 5 illustrate a practical embodiment of developer apparatus according to the invention and substantially conforming to the arrangement shown diagrammatically in FIGURE 1; and the same reference numerals are used where appropriate. The developer apparatus shown in FIGURES 4 and 5 comprises side walls 5 each provided at its forward end with an arcuate edge piece 4- for engagement with a drum (not shown). A circular rear wall 6 of the apparatus is provided with a bearing 6' for a shaft 8 of a rotary elevator which also comprises a hub 8 mounted on the shaft 8 for rotation therewith and a circular disc 7 round the periphery of which are mounted eight scoops 9. At their forward ends, the scoops 9 are closed by an annular disc 9' which is secured to them. Thus the shaft 8, hub 8', disc 7, scoops 9 and disc 9 form a rigid elevator assembly which rotates as a unit. This elevator assembly is housed in a chamber constituted by the rear wall 6, a cylindrical wall 25 and a partition wall 26 which is disposed parallel to the rear wall 6 and which is provided with a bearing 26' for the forward end of the shaft 8.

Mounted between the side walls 5,.by means of brackets 5' is a collector plate 15 which constitutes the bottom wall of a developer storage hopper 10 and which extends rearwardly, through an aperture 27 in the partition wall 26, into close proximity with the disc 7 of the elevator. The rearward part of the collector plate 15 is formed with an upturned portion 15 and with side wall portions 15 which abut against the partition wall 26 adjacent to respective side edges of the aperture 27 therein. Below the collector plate 15, a deflector plate 13 also extends between the side walls 5, its rearward part being provided with upwardly extending side wings 13' and projecting through an aperture 28 in the partition wall 26 to which it is secured by means of a bracket 29. Below the deflector plate 13 is a bottom plate 30.

The hopper 10, of which the collector plate 15 constitutes the bottom wall, is provided with a shutter 12 which, in its illustrated position, is in engagement with the plate 15 at the forward edge thereof. For raising the shutter 12, a solenoid 11 is provided, mounted on a cover plate 31 of the apparatus. The shutter 12, at each of its side edges, is slidable between guides 33, secured to the respective side walls 5, and a felt-covered plate 12 secured to the side walls 5 by brackets 32, which bears against the shutter 12 to provide a seal. At its upper edge, the shutter 12 is secured to an armature 11' of the solenoid 11, and to a pair of rods 34 adjacent the respective guides 33. Each rod 34 carries an anchor pin 35 for one end of a respective tension spring 36, the other end of which is anchored on a respective stop 37 adjustably secured on the respective guide 33. The springs 36 normally hold the shutter 12 in its illustrated position, but when the solenoid is energised it raises the shutter 12. The extent to which the shutter 12 can open may be controlled by various means (not shown) such as, for instance, adjusting the solenoids.

The developer apparatus shown in FIGURE 4 is provided with a replenisher 17, like that shown in FIGURE 3, which in FIGURE 4 is not shown in detail except that the flick rod 23 and part of the brush 22 are visible.

The operation of the developer apparatus shown in FIGURES 4 and 5 is substantially as already described with reference to FIGURE 1. The rotary elevator and its main shaft 8, connected to the main drive means of the reprographic apparatus which comprises them, rotate continuously whenever the reprographic apparatus is switched on, i.e. whenever the main drive means is operative to rotate the drum with which the developer apparatus cooperates. Initially, with the shutter 12 closed, the hopper contains a charge of developer, preferably carrier particles carrying developer powder; and the rotation of the elevator while the shutter 12 is still closed ensures that the hopper is fully charged before the shutter 12 opens. At an appropriate time determined by control circuitry of the reprographic apparatus, for example when the lead-ing edge of a document fed into the reprographic apparatus to be copied reaches and actuates an appropriately positioned microswitch included in said circuitry, the solenoid 11 is energised and opens the shutter 12 to the extent permitted by the stops 37, thereby allowing developer to cascade from the hopper 10 over the drum surface (not shown in FIGURE 4) to develop a latent electrostatic image, formed thereon, of the original document being copied. After a time interval determined by the control circuitry, for example on the said rnicroswitch being released as the trailing edge of the original document being copied passes it, the solenoid 11 is de-energised and the shutter 12 closes again. The hopper 10 contains more than enough developer, initially, to maintain the developer cascaded during the whole interval in which the shutter 12 is open; as will be evident, this interval may be equal to, but will not normally be more than, the time required for one complete rotation of the drum. The developer, after cascading over the drum, falls on to the deflector plate 13 and is directed thereby through the aperture 28 into the lower part of the chamber in which the rotary elevator is housed, whence it is returned by the rotary elevator to the hopper 10, the scoops 9 scooping up developer which has been delivered through the aperture 28 and delivering it on to the rearward end of the collector plate 15 as already described with reference to FIGURE 1. Any developer which might chance to miss the plate 13 would be caught and collected by the bottom plate 30. The replenisher device 17, like the shutter 12, is activated by suitable circuitry to operate only when required.

FIGURE 5 (from which the partition wall 26 and its apertures 27 and 28 have been omitted to avoid obscurity) shows the disposition of the scoops 9 round the elevator, and also shows the deflector plate 13 and the storage hopper collecting plate 15 and their disposition relative to the elevator. The scoops may be of any convenient shape and design, that configuration illustrated being particularly suitable. It will be seen that, as the scoop reaches the collecting plate 15, the developer starts to fall out on to the plate, and continues to discharge gradually almost until the scoop reaches the other side of the collecting plate. It will be appreciated that the elevator may be provided with as many scoops as may be necessary to achieve a suitably uniform and continuous flow of developer. It is important that the elevator should rotate at a suitable speed, for if it goes much too fast the developer is carried round by centrifugal force and scarcely discharged at all, if moderately fast then the bulk of the developer is discharged at the far end of the collecting plate, and if it goes too slow, the bulk of the developer is discharged at the near end of the collecting plate. Refinements of distribution could if desired be achieved by shaping the profile of the collecting plate, but it is found that in practice a plane plate 15 is satisfactory, provided the rotational speed of the elevator is suitably chosen.

There is always a possibility that some developer discharged from the scoops 3 will fall past the collector plate 15, and to guide such developer back to the bottom of the elevator housing, without allowing it a long free fall, there is provided an arcuate guard plate 38 secured to the partition wall 26 by means of a bracket 39.

What we claim is:

1. Developing apparatus for supplying developer material to an electrostatographic surface to cascade thereover and develop a latent image carried thereon, and for recirculating the developer material for subsequent reuse, comprising deflector means arranged to guide to a lower region developer material falling from the said surface after cascading thereover, conveyor means arranged to raise such developer material from said lower region and to discharge it at an upper region, a hopper comprising an inclined base having a rear end disposed below the said upper region to collect the developer material discharged there and a front end disposed obliquely below said rear end whereby developer material collected on the rear end moves by gravity towards the front end to be discharged therefrom to the said surface, a shutter arranged to co-operate with the hopper base near the front end thereof to prevent discharge of developing material therefrom, and means controlled separately from and independently of operation of said conveyor means for opening the shutter to allow such discharge from said hopper when required.

2. Developing apparatus as claimed in claim 1 and including replenisher means, arranged to discharge on to the hopper base and on to developer material thereon, for replenishing the developer material.

3. Developing apparatus as claimed in claim 1 wherein the conveyor means comprises a wheel-like member having scoops arranged round its periphery, the wheel-like member being rotatable about an axis which is perpendicular to the front edge of the hopper base.

4. Developing apparatus as claimed in claim 3, wherein the conveyor means is enclosed within a stationary housing the lower part of which encloses the said lower region, and the periphery of the conveyor means is open between mutually adjacent scoops.

5. Developing apparatus as claimed in claim 3 and including a rearwardly open housing which encloses the forward parts of the hopper and of the deflector means with the rearward parts thereof projecting rearwardly therefrom, wherein the wheel-like member encloses the scoops rearwardly and peripherally and an annular rotation-permitting seal is provided between the said housing and a forward part of the wheel-like member.

6. Developing apparatus as claimed in claim 1, wherein the shutter is spring-urged to close and is connected to a solenoid to be opened on energization thereof.

7. Reprographic apparatus comprising a cyclically movable electrostatographic surface and developing apparatus for supplying developer material to said surface to cascade thereover and develop a latent image carrier thereon, and for recirculating the developer material for subsequent reuse, said developer apparatus comprising deflector means arranged to guide to a lower region developer material falling from the said surface after cascading thereover, conveyor means arranged to raise such developer material from said lower region and to discharge it at an upper region, a hopper comprising an inclined base having a rear end disposed below the said upper region to collect the developer material discharged there and a front end disposed obliquely below said rear end whereby developer material collected on the rear end moves by gravity towards the front end to be discharged therefrom to the said surface, a shutter resiliently urged to cooperate with the hopper base near the front end thereof to prevent discharge of developing material therefrom, and means for opening the shutter intermittently during continuous operation of said conveyor means.

8. Reprographic apparatus as claimed in claim 7, wherein the said hopper contains, immediately prior to opening of said shutter, sufiicient developer material to be incompletely emptied 0n the shutter being held open during one complete cyclical movement of said electrostatographic surface.

References Cited CHARLES A. WILLMUTH, Primary Examiner.

P. FELDMAN, Assistant Examiner. 

